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How can a detector establish that an unseen particle changes identity? The Super-Kamiokande atmospheric-neutrino experiment compares different travel paths; the Sudbury Neutrino Observatory compares different interaction channels. Both infer neutrino flavor from reaction products and calibrated responses. Their complementarity connects particle detection to neutrino oscillation, neutrino mass and neutrino astronomy.

Takaaki Kajita and Arthur B. McDonald shared the 2015 physics Nobel Prize. These were collaboration achievements: Yoichiro Suzuki's Super-Kamiokande work included the solar neutrino analysis, and George Ewan helped establish and lead the Sudbury Neutrino Observatory.^[ref][ref]

The older Kamiokande account explains water Cherenkov neutrino reconstruction; Raymond Davis Jr.'s Homestake experiment explains why a deficit in an electron neutrino channel alone leaves a source-versus-propagation ambiguity. Complementary channels can break that ambiguity.

Awarded in equal shares to Takaaki Kajita and Arthur B. McDonald for discovering neutrino oscillations, showing that neutrinos have mass.^[ref]

Takaaki Kajita contributed to the Super-Kamiokande observation of atmospheric neutrino oscillations. Muon neutrinos arriving from below had crossed a much longer path through the Earth than those produced overhead. The direction-dependent deficit therefore tested propagation, while comparisons with electron-like events helped constrain possible production or detector explanations. The 1998 report found the pattern consistent with conversion between muon neutrinos and tau neutrinos.^[ref]

A physicist researching atmospheric neutrinos and neutrino oscillations.^[ref]